Based on potentials of Platinum electrodes in conjunction with a Calomel reference electrode, a servo controller was used to meter trickling filter secondary wastewater application to soil columns. The controller 'optimized' denitrification by adjusting the frequency of application as a function of the potential voltage observed 6 cm below the soil surface and duration of each application as a function of the potential 30 cm below the surface of four Chigley gravelly loam soil columns. Digested municipal wastewater sludge was added to 3 of the 4 columns at a rate of 7.5 metric tons (carbon)/hectare in an upper 30 cm layer of the profile. The servo controller applying wastewater to the column with no sludge requested wastewater continuously. This column converted essentially all TKN-N to NO3-N. The conversion of TKN to NO3 took place in the upper 3 cm of the profile. Under the experimental conditions, the disappearance of solution N in the column without sludge was about 45%. Addition of sludge to the profile increased the apparent denitrification such that the total N removal was greater than 90%.